Numerical predictions of cratering and scabbing in concrete slabs subjected to projectile impact using a modified version of HJC material model

• HJC model is modified for predicting cratering and scabbing of concrete slab under projectile impact.
• Modifications are validated by comparing with the available test data.
• DIF for tension and fracture strain are important for scabbing simulation.
• DIF for tension and the ratio of current to compressive meridians are crucial for cratering simulation.

The HJC material model, which has been widely used for numerical predictions of projectile penetration, is modified for the improved numerical simulations of the cratering and scabbing phenomenon in concrete slabs subjected to projectile impact. Four modifications, i.e. the modified yield surface, introduction of the tensile damage, introduction of Lode-angle dependency and modified strain-rate effect, are presented. The modified HJC model is implemented into the finite element code LS-DYNA through user defined material model. The improved performances due to the modifications are firstly demonstrated by single finite element numerical tests. And then several sets of projectile perforation experiments, in which the projectile mass, impact velocity and concrete slab thickness vary, are simulated by the modified HJC model, where corresponding predictions of the original HJC model are also presented to demonstrate the improved simulation of the cratering and scabbing phenomenon. Sensitivity analysis of three independent parameters that govern the tensile dynamic behavior of the modified model shows that the fracture strain and dynamic increase factor for tension are crucial for the correct modeling of the scabbing phenomenon, and the dynamic increase factor for tension as well as the ratio of the current meridian to the compressive meridian are important for the simulation of the cratering phenomenon.